Tuned circuit



Jan. 10, 1939. E. E. wlcKl-:RSHAM 2,143,812

TUNED CIRCUIT Original Filed March 29, 1933 i, l' lllllli 21 msm/HSPatented Jan.10, 1939 UNITED STATES PATENT OFFICE Divided and thisapplication January 4, 1938, Serial No. 183,385

5 Claims.

This application is a division of my copending application Serial No.663,298, flied March 29, 1933.

My ilrst object of this invention is to provide a 5 tuned circuit inwhich the cores of the various magnetic components of radio receivingand broadcasting sets consist of a nely divided metal having arelatively high electrical resistance, and good magnetic quality, so asto shorten the nat- 1o ural air gap length of the magnetic circuit inthese various magnetic components of such sets.

Another object is to produce a practically closed magnetic circuit forcoils and transformers of a non-corrosive, flnely divided metal which 15may be poured dry into a coil housing to form a magnetic unit of smallcompact form which may be easily and cheaply constructed.

Another object is to produce a magnetic circuit of a nely divided,non-corrosive metal hav- 20 ing high magnetic properties and whosecontact resistance between the various metal particles is high enough toprevent or reduce to a minimum any eddy currents which may be inducedtherein.

25 A further object is to produce in a tuned circuit certain componentsof an electrical instrument adapted to receive short wave, broadcast, orlong wave frequencies, the magnetic components of which, comprises oneor more coils in a each `unit having a combined core and shieldtherefor, composed of a finely divided magnetic material such asmagnetite, which is commonly called black sand, such as is found inlarge deposits along the Pacic coast and else- 35 where.

I attain these objects by constructing the tuned circuit, as illustratedin the accompanying drawing, in which:

Fig. 1 shows a fragmentary circuit of a type to o which my invention maybe applied.

Fig. 2 `is a vertical sectional elevation of a transformer having asingle winding, a combined metallic core and shield therefor, of theloose dry type, and a housing for the core and the coil 45 member.

Fig. 3 is a vertical sectional elevation of a transformer having acombined core and shield therefor, of the moulded type, lenclosed in ahousing.

50 Fig. 4 is a plan sectional view on line 4-4 of Fig. 3; and,

Fig. 5 is a vertical sectional elevation of a transformer including atwo circuit coil which is embraced by a combined magnetic core and 55shield therefor, all enclosed in a housing.

(Cl. Z50-40) In addition to these objects as set forth above, otherobjects will be apparent in the following specification:

I will state here and now that I am aware that metallic cores for coilsand transformers 5 have been used, including the so-called iron cladtype of magnetic core; also, that iron cores have been and are usedtoday in transformers employed as intermediate amplifiers in radio setsemploying the superheterodyne principle; and that iron cores of thelaminated type have been and are used in audio transformers,l chokecoils, and, in the magnetic components of loudspeakers, or reproducers;but, I am not aware that iron having the same characteristics 16 andphysical form as that of magnetite, which is generally termed in thegold mining districts,. "black sand, or that magnetite or black sand hasever been used as a material to form the cores of electro-magneticcoils, transformers, 20 loudspeakers, and especially those used in theart of manufacturing radio receiving and/or broadcasting equipment.

Referring to Fig. l, i-i'-| represent the radio frequency transformersof my preferred form as being positioned in an electrical circuit, theybeing particularly illustrated in Fig. 2 and Fig. 3. In Fig. l, 2 is theaudio transformer, while 3-3 represent the choke coils in this circuitand 4 represents the magnetic component 30 of the loudspeaker orreproducer of the character illustrated in Fig. 6 of my said copendingapplication Serial No. 663,928, allowed July 25, 1938.

Referring more particularly to Fig. 1, the first two tubes are highfrequency amplifiers whereas the third tube is a detector and the fourthtube a low frequency amplifier. The input to the rst tube comprises aresonant circuit made up of an inductance L. and a condenser C.. Theinput ofthe second tube includes the resonant circuit made up of coil L.and condenser C, while the input of the `third tube or detector includesthe resonant circuit comprising coil L. and condenser C.. The threecondensers C., C, and C'. are variable so that the respective circuitsin which these condensers are located may be made to resonate at apredetermined carrier frequency.

It should be noted that the detector tubeV is provided with a grid leakR. and condenser C, arrangement In the circuit arrangement shown 50 thecarrier frequency is present up to the detector.

In order that others skilled in this art may make and use my invention,in spirit, I will describe the construction of the various magneticcomponents as set forth in the drawing. 55

Referring to Fig. 2, the coil member 5 is preferably formed by windingthe desired number of turns of wlre upon a nonconductive form, or tube,6 and bringing the free ends of said wire 1--1 out through restrictedtubes 8-8', to which other wires of an electrical circuit may be'attached. At some desired point intermediate the ends of coil 5, a tapwire X is brought out from coil 5 through tube 8B, which may beconnected to a. source of electrical energy, not shown. The coil ispreferably supported inside of housing 9 by tubes 8--8' and 8B. It willbe seen that the housing for the coil is provided with a cover III whichis :normally held in position on housing 9 by screws II-II'.

In carrying out the spirit of my invention, I will assume that the coil5 has been formed and properly insulated as at Y, by a covering ofcloth, paper, or wax, and suspended in housing 9 and that the cover I Ilhas been removed therefrom. The next step, I prefer to pour a quantityof magnetite or black sand, into housing 9, sufficient to completelysubmerge the coil 5 and to practically flll said housing to the topthereof, to form a combined core and shield, and thus also form a.closed magnetic circuit. The cover I may now be replaced on housing 9and secured by screws II-I I' or by other means. The magnetic coil ortransformer unit is now completed and ready for use.

Fig. 3 shows a coil or transformer l2 having its combined core andshield formed in two parts, upper and lower, as shown at I3--I3' thatare composed of magnetite or black sand, which has previously beenwetted or moistened with a quick drying binding material such as shellacand subsequently baked to dryness in a metal mould, not shown, so thatthe moisture in the binder may be evaporated and the cores become dry,hard, and self-supporting.

Each section of said core I3--I3' has an annular channel I4-I4 formed inthe inner faces thereof, and having a central post I5 extending from thedepth of said annular channel to a point in the plane of said faces I6of cores I3'-I3' which are adapted to support the coil I2 and its formIl as is clearly shown in Fig. 3.

Fig. 4 shows the coil in said annular channel and also the manner inwhich the combined core and shield of magnetite or black sand,completely engulfs and encloses the coil I2 and its form I1; it being aView taken on line 4;-4 of Fig. 3.

Fig. 5 shows and illustrates a transformer of the so-called audio time.the current carrying components of which are preferably formed in thetwo parts termed primary and secondary coils, as at I8 and I9,respectively. 'I'he combined core and shield 20 forming practically aclosed magnetic circuit may be formed according to the method describedin the forming of the corresponding component illustrated in Fig. 2, thecoils I 8-l9 are preferably wound on a form of insulating material 2land then covered and sealed by a exible tubular insulating form such asshown at 22 to effectively prevent the various metallic particles whichform the core and shield from making physical contact with the windingsof the coils I8-I9. The insulation 22 may be of any suitable materialsuch as paper.

Referring again to Fig. 5, it will be readily understood that the coiland core housing 23 is adapted to receive and enclose both the coil andcore components of the transformer and that a cover 24 is readilyAdetachable so that the said components may be readily installed andmounted therein.

One of the eects of the presence of magnetite in the field of a coilthrough which current is flowing, is: that for the same number of turnsin a coil, its inductance is increased, and consequently a coil having aclosed magnetic circuit of magnetite will require a lesser number ofturns of wire and proportionately reduce the ohmic resistance, which,for coilsand transformers such as are used in radio apparatus, isadvantageous.

One advantage gained by the use of these cores for transformers whenconstructed of magnetite, as described, is the ease with which two ormore coils may be inductively matched. The magnetite, as used, is nelydivided, and so pure that oxidation does not occur, and that due to thethousands of particles of the magnetite or black sand, included in asuillcient quantity of this material to make or construct a core, asdescribed, it is apparent now that by the addition of a few grains ofmagnetite to the core of a coil or transformer the inductance thereofwillV be increased, and conversely when a few grains are deleted fromthe core mass the inductance of said coil will be decreased.

Thus, in order that two or more coils of the character described be madeto have the same inductance, it is only necessary` to either add to, ortake away a sufficient quantity of magnetite or black sand from the coreor one or more of said coils, to equalize their inductances.

I have found by experimentation that coils having cores constructed inaccordance with the spirit of my invention are very selective withrespect to the short wave band of radio frequencies, and I also havefound that when a radio broadcast receiver having the usual multlplicltyof tuned circuits and employing theseA coils as tuning inductances, thatthe selectivity is adequate and the receiver is capable of operation incongested districts.

In addition to these above advantages, the tonal quality of reproductionis greatly improved, which is due in part, to the fact that all eddycurrents are immediately dissipated and localized by the high contactresistance between the magnetite particles forming the cores andincidental to the minute physical dimensions of the particles ofmagnetite used in said cores the effective length of the air gap in themagnetic path is shortened and also that these cores are not easilymagnetically saturated, consequently, there is no distortional effectsheard in the reproducer. l

Inasmuch as the particular wiring scheme I have shown in Fig. 1 toillustrate the application of these various components which lI haveheretofore described form no part of this invention and also that theprinciples governing the workings of the coils, transformers, andloudspeakers, or reproducers, are well understood.

by .those skilled in this art, therefore, I deem it unnecessary to makefurther explanations in this regard.

I have constructedand used coils and cores in tuned circuits asdescribed herein and am not familiar with ,all the phenomena which takesplace therein, but I do know the results obtained by their use areindeed gratifying and I realize that these cores and shields may be madein many other physical forms employing the use of magnetite, or whatisknown as black sand,

and intent of the following claims to be limited only by the state ofthe art to which they pertain.

I claim:

1. A circuit resonant to a high carrier frequency and including aninductance coil provided with a core composed of comminuted nativemagnetite, retaining its native magnetic properties.

2. A circuit resonant to a high carrier frequency including aninductance coil and a condenser in circuit therewith, said inductancecoil being provided with a. core composed of comminuted native magnetiteretaining its native magnetic properties.

3. A circuit resonant to a high carirer frequency including aninductance coil provided with a core composed of comminuted nativemagnetite retaining its native magnetic propert1es .and a condensershunted across said inductance coil.

4. A circuit resonant to a high carrier frequency and comprising aninductance coil and an element variable to tune said circuit over a bandof frequencies, said coil having a. core composed of comminute nativemagnetite mixed with a binder for maintaining the magnetite in a;predetermined core shape.

5. A circuit resonant to a high carrier frequency comprising aninductance coil and a variable condenser for tuning said circuit over aband of frequencies, said coil having a core composed of comminutednative magnetite mixed 'a predetermined core shape.

ELMER. E. WICKERSHAM.

